Numerous types of wastewater or produced water have relatively high concentrations of organics, silica, boron, hardness, suspended and dissolved solids. For example, oil recovery operations produce water that includes high concentrations of these contaminants. If such wastewater or produced water is to be used in high purity applications, such as a feed to a boiler or once through a steam generator or process water, then there must be a substantial reduction in silica, total hardness, dissolved solids and organics.
Ion exchange processes and reverse osmosis processes have been used for desalting produced water or wastewater. Current practices involving the operation of reverse osmosis systems usually maintain a neutral pH condition, which is a pH of approximately 6-8. In the case of feed water produced by oil and gas operations, the recovery across reverse osmosis systems is often limited by scaling due to silica or fouling due to organics. That is, high concentrations of silica in the feed water tend to scale the reverse osmosis membranes due to the concentration of silica exceeding solubility limits. Organics that exceed solubility limits also tend to foul the reverse osmosis membranes. Scaling due to silica and fouling due to organics can cause substantial down time of the reverse osmosis unit or units, requiring frequent cleaning, replacement and maintenance. The maintenance is obviously expensive and the down time is costly and inefficient.
In addition, in the case of produced water, for example, processes are designed to remove silica and boron. These contaminants are often present in the form of weakly ionized salts, sicilic acid and boric acid, and generally reverse osmosis membranes are not efficient in rejecting such weakly ionized salts.
Therefore, there has been and continues to be a need for an economical process for treating wastewater or produced water that reduces fouling due to organics, reduces scaling due to silica, and which will efficiently reduce the concentrations of silica, organics, dissolved solids and hardness in the wastewater or produced water.